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Methane Concentration (methane + concentration)

Distribution by Scientific Domains

Polymers and Materials Science	33%

Selected Abstracts

The active methanotrophic community in hydromorphic soils changes in response to changing methane concentration

ENVIRONMENTAL MICROBIOLOGY, Issue 2 2006
Claudia Knief
Summary Methanotrophic communities were studied in several periodically water-saturated gleyic soils. When sampled, each soil had an oxic upper layer and consumed methane from the atmosphere (at 1.75 ppmv). In most gleyic soils the Km(app) values for methane were between 70 and 800 ppmv. These are higher than most values observed in dry upland soils, but lower than those measured in wetlands. Based on cultivation-independent retrieval of the pmoA -gene and quantification of partial pmoA gene sequences, type II (Alphaproteobacteria) methanotrophs of the genus Methylocystis spp. were abundant (> 107pmoA target molecules per gram of dry soil). Type I (Gammaproteobacteria) methanotrophs related to the genera Methylobacter and Methylocaldum/Methylococcus were detected in some soils. Six pmoA sequence types not closely related to sequences from cultivated methanotrophs were detected as well, indicating that diverse uncultivated methanotrophs were present. Three Gleysols were incubated under different mixing ratios of 13C-labelled methane to examine 13C incorporation into phospholipid fatty acids (PLFAs). Phospholipid fatty acids typical of type II methanotrophs, 16:0 and 18:1,7c, were labelled with 13C in all soils after incubation under an atmosphere containing 30 ppmv of methane. Incubation under 500 ppmv of methane resulted in labelling of additional PLFAs besides 16:0 and 18:1,7c, suggesting that the composition of the active methanotrophic community changed in response to increased methane supply. In two soils, 16:1 PLFAs typical of type I methanotrophs were strongly labelled after incubation under the high methane mixing ratio only. Type II methanotrophs are most likely responsible for atmospheric methane uptake in these soils, while type I methanotrophs become active when methane is produced in the soil. [source]

Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning Mechanisms

ADVANCED FUNCTIONAL MATERIALS, Issue 24 2009
Tao Liu
Abstract Three groups of free-standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high-resolution electron back-scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp3 hybridization of the bond in the CH4 molecule that is used as the deposition medium. [source]

Real-time quadrupole mass spectrometer analysis of gas in borehole fluid samples acquired using the U-tube sampling methodology

GEOFLUIDS (ELECTRONIC), Issue 3 2006
B. M. FREIFELD
Abstract Sampling of fluids in deep boreholes is challenging because of the necessity of minimizing external contamination and maintaining sample integrity during recovery. The U-tube sampling methodology was developed to collect large volume, multiphase samples at in situ pressures. As a permanent or semi-permanent installation, the U-tube can be used for rapidly acquiring multiple samples or it may be installed for long-term monitoring applications. The U-tube was first deployed in Liberty County, TX to monitor crosswell CO2 injection as part of the Frio CO2 sequestration experiment. Analysis of gases (dissolved or separate phase) was performed in the field using a quadrupole mass spectrometer, which served as the basis for determining the arrival of the CO2 plume. The presence of oxygen and argon in elevated concentrations, along with reduced methane concentration, indicates sample alteration caused by the introduction of surface fluids during borehole completion. Despite producing the well to eliminate non-native fluids, measurements demonstrate that contamination persists until the immiscible CO2 injection swept formation fluid into the observation wellbore. [source]

Synthesis and characterisation of NCD films on 10 × 10 mm2 and deposition on 2 inch wafer using rotating substrate-holder set-up

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2008
S. Saada
Abstract In this study, we compare NCD films on 10 × 10 mm2 silicon substrates synthesised with high methane concentration and NCD films synthesised with prolongated bias during the growth step. Further, we performed in-situ sequential XPS analysis (carbon binding state) using an UHV surface analysis system connected to the MPCVD reactor. AFM and HRSEM were used to characterize films morphology. Using the same substrate holder, NCD films have been deposited on silicon 2 in wafers. To improve the homogeneity, a rotating substrate-holder set-up enabling biasing and heating of the stage has been developed and coupled with computer control of the process for a better reproducibility. UV-interferometry was performed to map the film thickness on 2 inches and quantify its thickness uniformity. Considering the symmetry of the system, AFM measurements were performed along the radius of the wafer to evaluate the surface homogeneity and its smoothness. The thickness uniformity of a NCD film of 1.6 µm deposited on 2 inch wafer is under 10% and the RMS roughness comprised between 13 and 14 nm. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Growth of Diamond Nanoplatelets by CVD,

CHEMICAL VAPOR DEPOSITION, Issue 7-8 2008
Hou-Guang Chen
Abstract Hexagonal, single-crystalline, diamond nanoplatelets synthesized by microwave plasma (MP)CVD on Au-Ge alloy and nanocrystalline diamond (nc-diamond) film substrates, respectively, are reported. On the nc-diamond matrix, hexagonal diamond nanoplatelets can grow to a thickness of as little as approximately 10,nm. The effects of various processing parameters, such as methane concentration, microwave power, and gas pressure, on the growth of diamond nanoplatelets are explored. High-resolution transmission electron microscopy (HRTEM) reveals that the diamond nanoplatelets contain multi-parallel twins, and the side faces of the platelets exhibit {100}/{111} ridge-and-trough structure. Anisotropic growth of diamond nanoplatelet is believed to result from the side face structure of the twinned platelets and intensive plasma reaction. [source]

A methane-driven microbial food web in a wetland rice soil

ENVIRONMENTAL MICROBIOLOGY, Issue 12 2007
Jun Murase
Summary Methane oxidation is a key process controlling methane emission from anoxic habitats into the atmosphere. Methanotrophs, responsible for aerobic methane oxidation, do not only oxidize but also assimilate methane. Once assimilated, methane carbon may be utilized by other organisms. Here we report on a microbial food web in a rice field soil driven by methane. A thin layer of water-saturated rice field soil was incubated under opposing gradients of oxygen and 13C-labelled methane. Bacterial and eukaryotic communities incorporating methane carbon were analysed by RNA-stable isotope probing (SIP). Terminal restriction fragment length polymorphism (T-RFLP) and cloning showed that methanotrophs were the most prominent group of bacteria incorporating methane carbon. In addition, a few Myxobacteria -related sequences were obtained from the ,heavy' rRNA fraction. Denaturing gradient gel electrophoresis (DGGE) targeting 18S rRNA detected various groups of protists in the ,heavy' rRNA fraction including naked amoeba (Lobosea and Heterolobosea), ciliates (Colpodea) and flagellates (Cercozoa). Incubation of soil under different methane concentrations in air resulted in the development of distinct protozoan communities. These results suggest that methane carbon is incorporated into non-methanotrophic pro- and microeukaryotes probably via grazing, and that methane oxidation is a shaping force of the microeukaryotic community depending on methane availability. [source]